One type of apparatus used for folding paperboard blanks involves a stationary rail. The rail is configured and positioned so that, as a blank is conveyed through the apparatus, the rail bears on an outboard panel of the blank at its leading edge and causes that panel to swing relative to an adjacent panel along a crease between the panels. The apparatus operates acceptably during an initial portion of the folding. Such is not the case with the last portion of a 180 degree fold. During this last portion of folding, the resistance to folding greatly increases due to material interference in the crease. When this occurs, the force of the rail at the leading edge of the panel being folded, with more than acceptable frequency, causes a fold slanted from the direction of feed ("fish tailing") and/or the occurrence of folding at a cross-machine crease (corrugator score) leading to a jam up.
In an attempt to minimize the occurrence of "fish tailing", the apparatus described above has been modified to replace a last portion of the stationary rail with a twisted, high friction material, moving belt. Like the stationary rail, the moving belt folds by bearing on the leading edge of an outboard panel as the blank is conveyed. But, unlike the stationary rail, it pulls such panel in an attempt to match speeds with the conveyor to prevent the occurrence of "fish tailing". Such speed matching is difficult to obtain on a consistent basis. Thus, this modification does not entirely eliminate "fish tailing" and can even cause "fish tailing". Moreover, with this modification, folding at a cross-machine crease is still a problem.
Apparatus exist or are known which include means rotating in time with the machine and having axis of rotation perpendicular to the direction of travel. Such means bear on interior portion of a panel to cause rather abrupt folding (a large amount of folding during a relatively short distance of board travel). Such abrupt action can result in panel damage especially when corrugated blanks are being processed at high rates of travel. Such apparatus can also involve an impacting (i.e. slapping) action which can harm a blank.